This invention relates to electronic systems, and more particularly to the detection of an electronic system being operated at increased voltages associated with operation outside a specified frequency range.
Some systems and circuits are designed to operate over a range of frequencies. For example, microprocessors are often designed to operate at frequencies between 200 megahertz and 500 megahertz. However, a microprocessor manufacturer may only test and warrant a microprocessor for operation at frequencies of less than 300 megahertz. To ensure that the microprocessor is not operated above the tested and warranted frequency range, the manufacturer may attempt to design circuits into the microprocessor that directly detect overfrequency operation and disable the microprocessor when the overfrequency operation is detected. Unfortunately, these circuits require at least one bulky off chip component, such as a stable frequency source, and are subject to tampering.
In general, to operate a digital system, such as a microprocessor, at a higher frequency, the power supply voltage provided to the digital system is increased. The reason for this is that the transistors that make up the logic circuits in the digital system can switch faster when operated at a higher power supply voltage level. Operating a microprocessor at a higher frequency permits the microprocessor to perform more work in a given amount of time. Since increasing the power supply voltage provided to the microprocessor improves performance, and since the cost of increasing the power supply voltage is low, some system manufacturers design systems that operate microprocessors and other digital and analog systems outside their intended and warranted frequency range by increasing the power supply voltage.
For these and other reasons there is a need for the present invention.